Aluminum-molybdenum-titanium master alloy

ABSTRACT

THIS INVENTION RELATES TO MASTER ALLOYS CONTAINING ABOUT 35 TO 50% MOLYBDENUM, ABOUT 6.5 TO 15% TITANIUM, BALANCE ALUMINUM, AND NOT MORE THAN ABOUT 0.1%, BY WEIGHT, OXYGEN, WHICH ARE USED IN PREPARING BASE ALLOYS.

United States Patent O1 Ffice 3,725,054 Patented Apr. 3, 1973 3,725,054 ALUMINUM-MOLYBDENUM-TITANIUM MASTER ALLOY Frederick H. Perfect, Wyomissing, Pa., assignor to Reading Alloys, Inc., Robesonia, Pa.

No Drawing. Filed Aug. 30, 1971, Ser. No. 176,322 Int. Cl. C22c 21/00 U.S. Cl. 75-134 F 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to master alloys containing about 35 to 50% molybdenum, about 6.5 to 15% titanium, balance aluminum, and not more than about 0.1%, by weight, oxygen, which are used in preparing titanium base alloys.

BACKGROUND OF THE INVENTION Titanium base alloys containing aluminum and molybdenum are widely used, one application being found in the aircraft industry where such alloys are utilized in both structural and engine components. Titanium base alloys are commonly prepared by alloying titanium sponge with a master alloy containing the elements desired in the final alloy. Titanium sponge is alloyed with the master alloy by first forming a mixture of the sponge and master alloy. This mixture is compacted and assembled into an electrode by welding. The electrode is then melted in a vacuum furnace forming the desired titanium base alloy. To form the mixture of titanium sponge and master alloy, it is necessary that the alloy be friable or brittle so that it can be easily sized to a state which mixes well with the titanium sponge.

In attempting to form a master alloy containing about 38% molybdenum, balance aluminum, it was found that such an alloy was malleable or ductile and, thus, could not be sized for mixture with titanium sponge. It thus became desirable to add an element to the molybdenum-aluminum alloy which would render the alloy brittle so that it could easily be sized for mixture with the titanium sponge. Titanium has been found suitable for this purpose.

Aluminum base alloy powders containing molybdenum and titanium are described in US. Pats. Nos. 2,966,733 and 2,966,735. The company to which the present application is assigned in part has produced master alloys containing 40 to 45% aluminum, 50 to 55% molybdenum, and less than 5% titanium for use in preparing titanium base alloys for many years. The titanium base alloys produced with this master alloy differ in composition and properties from those produced with the master alloys of this invention.

In producing master alloys for production of titanium base alloys, it is important that the master alloy be fairly easily melted and not have too high a melting temperature so that it will easily and uniformly combine with the titanium base metal. The master alloy should also be of high purity, free of contaminants Which would find their way into the titanium alloy. It is also advantageous if the master alloy have a low oxygen content, i.e. less than 0.1%, by weight.

Accordingly, it is the object of this invention to provide an aluminum-molybdenum-titanium master alloy for use in the manufacture of titanium-base alloys which is friable, relatively low melting, of high purity, containing less than 0.1%, by weight, oxygen, and relatively easy and inexpensive to make.

DETAILED DESCRIPTION OF THE INVENTION According to this invention, there is provided a master alloy consisting essentially of about 35 to 50% molybdenum, about 6.5 to 15% titanium, balance aluminum,

said alloy containing not more than 0.1%, by weight, oxygen.

The alloys of the present invention are readily produced by the aluminothermic reduction of molybdic oxide (M00 and titanium dioxide With excess aluminum, the reduced metals combining with the aluminum forming the desired master alloy. It is critical that the master alloy contain titanium in the amount stated above (6.5 to 15%, by weight) so that it can be sized for easy mixture with titanium sponge. The titanium content is also thought to aid in the solubility of the molybdenum in the titanium base alloy.

Various apparatus may be employed in producing the master alloys of this invention. For example, the reaction may be caused to take place in a water-cooled copper pot or crucible. The use of a water-cooled copper furnace avoids all refractory contamination problems. In addition, inasmuch as the reaction produces two separate layers, i.e. an alloy layer covered by a layer of molten slag containing flux, it may be desirable to employ a reaction vessel having a taphole toward the bottom to aid in separation of alloy from the flux. If desired, the reaction vessel may be so constructed as to permit carrying out the aluminothermic reaction in an atmosphere of an inert gas, such as argon. A preferred type of reaction vessel is a water-cooled copper vessel of the type described in Metallothermic Reduction of Oxides in Water-Cooled Copper 'Furnaces, by F. H. Perfect, Transactions of the Metallurgical Society of AIME, vol. 239, Sgst 67, pp.

In carrying out the process of this invention, the molyb- Y die oxide, titanium dioxide and aluminum may be reduced to relatively small size and intimately mixed so that the reaction will occur very rapidly and uniformly throughout the charge once it is ignited. More aluminum is added than is necessary to react with the metal oxides in order to produce an alloy of the metals molybdenum, titanium and aluminum.

Ignition of the reaction mixture may be effected by heating the charge above the melting point of the aluminum by an electric arc, gas burners, hot metal bar, or the like.

To be successful, substantially all the reaction products resulting from the ignition of the charge must be melted and remain in a molten state long enough to permit separation of the alloy from the slag, i.e. calcium aluminate. Since the separation is by Stratification due to gravity, it is necessary that the molten material has substantial fluidity. Fluidity of the slag may be obtained by inclusion in the charge of certain inorganic materials which act as a flux to lower the viscosity of the slag. Typical of these materials are lime and fluorspar, which form a molten flux at reaction temperatures for absorption of the aluminum slag. These materials generally remain unaffected by the reduction reaction.

The process of the present invention should be carried out with chemically pure molybdic oxide (molybdenum trioxide) containing 99+% of M00 or very pure calcium molybdate.

Advantageously, the present process does not require the use of chemically pure titanium dioxide. Thus, although pigment grade, commercially pure titanium dioxide which analyzes 99+% TiO is preferred, less pure Tio -containing material, such as native rutile, which analyzes about 96% TiO and contains as impurities minor amounts of the oxides of Fe, Si, Zr, Cr, Al and Ca, as well as S and P, can also be employed. Commercially pure TiO is preferably used to enhance the overall purity of the resulting alloy.

The aluminum should be of the highest purity which is commercially available. Chopped aluminum wire (a relatively pure conductor material) containing less than 0.005% boron can be employed. However, virgin aluminum powder which analyzes in excess of 99% of aluminum, is the preferred reducing agent and an alloy addition agent according to the present process.

Since the metal oxide and aluminum reactants may vary in purity, the proportions thereof to provide an alloy of the given composition will vary accordingly. For this reason, in this description and appended claim, the respective amounts of reactants are expressed in terms of the composition of the desired alloy. As stated hereinabove, the amounts of these reactions should be so proportioned to provide a master alloy containing from about 35 to 50% molybdenum, about 6.5 to 15% titanium, balance aluminum.

During the reaction, calcium aluminate slag is produced. As stated above, in order to aid in separating the slag from the alloy, the reaction is carried out in the presence of a molten flux which dilutes the slag and renders it in a more fluid form.

The molten flux which may be employed in the process of the present invention, may comprise one or more inorganic materials having a melting point below the temperature which the molybdic oxide and titanium dioxide react with the aluminum. This reflux must be capable of diluting the slag formed by the reaction to produce a less viscous slag which easily separates from the alloy. The readily available fluorides and chlorides of such metals as Ca, Ma, Al, and K, alone or in combination with other inorganic materials, are particularly suitable for forming slag-absorbing fluxes. A particularly preferred flux is one formed from lime and fluorspar wherein the weight ratio of the former to the latter is from about .5:1 to 2:1.

The amount of flux-forming constituents employed should be suflicient to provide an amount of molten flux capable of diluting the slag that is formed during the reduction of the oxides of molybdenum and titanium to provide a less viscous slag which is readily separated from the metal. Preferably, an excess of flux over that needed to obtain the desired viscosity reduction is used. This excess may generally be from about 0.5 to 2 times the weight of the slag formed in the process.

The resulting aluminum-molybdenum-titanium alloy contains less than about 0.1% oxygen, indicating the substantial absence of light density particles, such as alumina, titania, and calcia, particles which if contained in any substantial quantities in the master alloy, will be carried over into the ultimate titanium base alloy and structural components made therefrom. The presence of such light density particles in structural components made from titanium base alloys cannot be tolerated as they render such components unacceptable for use under high performance conditions such as encountered in aircraft construction.

To form titanium base alloys from the titanium-alumi-- num master alloy, the alloy is suitably sized to 10 mm. by down and blended with titanium sponge, in suflicient amounts to provide the desired molybdenum-aluminumtitanium alloy and compacted at room temperature to a convenient generally cylindrical shape. Several of such compacts are then welded together to form a size convenient for use as an electrode and the thus-formed electrode is electrically melted in a conventional manner to produce the desired alloy.

The following examples illustrate the above-described invention:

' EXAMPLE 1 The materials shown in Table I were combined and mixed together:

Table I Ingredient: Weight (lbs.) Molybdic oxide sublimed (M 80 TiO (pigment grade) '30 Aluminum powder 125 4 Ingredient: Weight (lbs.)

Lime (CaO) 20 Fluorspar (CaF acid grade) 10 After mixing, the charge was placed in a water-cooled copper furnace. The charge was ignited and runs for about one minute. The resulting alloy was tapped and the ingot produced weighed 136138 pounds. This ingot was easily crushed and sized to 10 mm. by down.

The analysis of the alloy is in Table II.

Following the procedure of Example 1, an alloy was prepared from the mixture shown in Table III.

Table III Ingredient: Weight (grams) Molybdic oxide (M00 800 TiO (pigment grade) 250 Aluminum powder 900 Lime (CaO) 350 Fluorspar (CaF The mixture was ignited and runs for 25 seconds, the ingot produced weighing 916 g. An analysis of the result ing alloy is shown in Table IV.

Table IV Percent Mo 48.63 T1 12.13 Al 37.41 0 0.11

EXAMPLE 3 Following the procedure of Example 1, an alloy was prepared from the mixture shown in Table V.

Table V Ingredient: Weight (grams) Molybdic oxide (M00 800 TiO (pigment grade) Aluminum powder 860 Lime (CaO) 350 Fluorspar (CaF W--. 100

The mixture was ignited and runs for 17 seconds, the ingot produced weighing 910 g.

An analysis of the resulting alloy is shown in Table VI.

Table VI Percent Mo 47.96 Ti 9.53 Al 40.36 0 0.03

EXAMPLE 4 Following the procedure of Example 1, an alloy was prepared from the mixture shown in Table VII.

5 Table VII Ingredient: Weight (grams) Molybdic oxide (M00 800 TiO (pigment grade) 125 Aluminum powder 840 Lime (CaO) 350 Fluorspar (CaF 100 The mixture was ignited and runs for 16 seconds, the ingot produced weighing 922 g.

An analysis of the resulting alloy is shown in Table VIII.

References Cited UNITED STATES PATENTS 2,966,733 1/1961 ToWner et al. 75138 X 2,966,735 1/1961 Towner et a1. 75--138 X L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner US. Cl. X.R. 

